This invention relates to an improved catalytic process for the hydrogenation of acyclic and cyclic carboxylic acid anhydrides to esters and lactones, respectively. More particularly, this invention relates to the foregoing process wherein the reaction takes place under mild conditions in the presence of an organometallic ruthenium trichlorostannate complex catalyst in homogeneous solution.
U.S. Pat. No. 3,957,827 to J. E. Lyons, issued May 18, 1976, describes the selective catalytic hydrogenation of acyclic and cyclic carboxylic acid anhydrides to esters and lactones wherein the catalyst is a ruthenium complex of the formula (I): ##STR2## where X is hydrogen, chlorine, bromine, iodine or lower alkyl; n is an integer of from 0 to 2, but when n is 2, X may be the same or different; L is a neutral ligand, olefin or CO; y is an integer of from 0 to 3, but when y is 2 or 3, L may be the same or different; R.sub.6, R.sub.7 and R.sub.8 are lower alkyl, cycloalkyl of from 5 to 15 carbon atoms, aryl, benzyl or a bidentate ligand, and each of the R groups may be the same or different; and x is an integer of from 1 to 3. The reaction occurs readily under mild reaction conditions in homogeneous solution and is characterized by good selectivity and yield, and does not proceed beyond ester or lactone formation.